A recent review study led by The University of Texas at Austin provides an overview of the planet's freshwater supplies and strategies for sustainably managing them.
Published in Nature Reviews Earth & Environment, the study highlights the connections between surface and groundwater and calls for diversified strategies for managing them both.

"I like to emphasize a lot of solutions and how they can be optimized," said lead author Bridget Scanlon, a senior research scientist at the UT Bureau of Economic Geology, a research unit of the Jackson School of Geosciences.

The study draws on data from satellites, climate models, monitoring networks and almost 200 scientific papers to analyze Earth's water supply, how it's changing in different regions and what's driving these changes. The study's co-authors include almost two dozen water experts from around the world.

According to the research, humans primarily rely on surface water. Globally, it accounts for 75% of irrigation and 83% of municipal and industrial supply annually. However, what we see at the surface is tightly connected to groundwater flow. In the United States, about 50% of annual streamflow starts as groundwater. And globally, surface water that seeps into the ground accounts for about 30% of annual groundwater supplies.

Human intervention can strongly influence the exchange in water between surface and groundwater sources. About 85% of groundwater pumped by humans in the U.S. is considered "captured" from surface water, which leads to declines in streamflow. At the same time, irrigation sourced from surface water can increase groundwater recharge as irrigated water seeps through the ground back to aquifers.

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